1. Field of the Invention
The present invention is directed to an ink printer head of the type composed of a stacked ink printer modules operating according to the edge-shooter principle and that are equipped with ink ejecting piezoelectric actuators.
2. Description of the Prior Art
Ink printer head of the above-described type are used in small, fast printers that are in turn a component of modern machines for franking postal matter or for printing addresses.
Differing from a standard office printer with line-by-line imprinting, the printing ensues in such smaller machines as a one-time franking imprint in one pass of the postal matter. The printing width determines the number of nozzles to be arranged in one column of the nozzle matrix, and thus also determines one dimension of the ink printer head. The capability of printing blocks having word and image characters is a feature available using such postage meter machines. Printer resolutions of approximately 200 dpi are required for assuring a good printing quality. This requires nozzle apertures having a width of 40 through 50 .mu.m. High demands are thus made on the precision of the nozzle division and the drive thereof. Given a standard block width of one inch, the adjustment error must be kept below 10 .mu.m.
German OS 42 25 799 discloses an ink printer head of the type initially described that is composed of a number of different modules, only one module thereof carrying the shared nozzle row at its end face. All modules have pressure chambers driveable by piezoactuators for ink ejection that are connected to the allocated nozzles via appropriately conducted channels. The connecting channels from module to module necessarily proceed orthogonally relative to the pressure chambers.
Although the advantage of only a single nozzle row is significant, the technological outlay for manufacturing the modules that differ from one another is still substantial.
Higher precision than that for the pressure chambers and a higher adjustment outlay are required for the connecting channels that proceed through a number of modules. The fact that the connecting channels have different lengths causes additional control problems. Although the advantage of only a single nozzle row is significant, the technological outlay for manufacturing the modules that differ from one another is still considerable.
German OS 26 49 970 also discloses an ink printer head that is composed of sandwiched individual, smooth plates having the same size. Successively arranged at both sides of a nozzle plate are an intermediate plate, two channel plates, a membrane plate and--at the outside thereof--piezoactuators.
The nozzle plate has one end face provided with tooth-like cut-outs that represent the nozzles or, respectively, nozzle apertures; compensation chambers or, respectively, recesses are present in the part of the nozzle plate lying therebehind for the purpose of decoupling the ink pressure chambers lying at both sides of the nozzle plate.
The intermediate plates has openings for the ink flow to the nozzles.
Ink or energy flow channels to the nozzles and admission channels for ink from an ink reservoir are located in the channel plates in the form of openings therein.
The pump plates have openings in registration with the compensation chambers in the nozzle plate, one part of these openings serving as a pump space and the other part serving as an ink flow channel.
In addition to their above-described function, the membrane plates serve the purpose of closing the system and also serve as a carrier for the piezoactuators.
The described arrangement essentially represents an ink printer head composed of two ink printer modules that are constructed mirror-symmetrically relative to one another and which share a nozzle plate. Piezoactuators are secured only at the two outside walls and piezoactuators that lie opposite one another are simultaneously driven.
Although the outlay of eleven plates is rather substantial, printer resolutions of only 24 dpi are achieved with this ink printer head because of the structure as well as due to the operating mode. A resolution of 192 dpi, however, is required for the above-described use in a franking machine.